Adds tests for mr_widget_rebase component

ee/app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_rebase.vue

@@ -124,7 +124,7 @@
             branch into source branch to allow this merge request to be merged.
           </span>
           <span
-            v-if="renderError"
+            v-else
             class="bold danger">
             {{rebasingError}}
           </span>

spec/javascripts/vue_mr_widget/components/mr_widget_rebase_spec.js

+import Vue from 'vue';
+import component from 'ee/vue_merge_request_widget/components/states/mr_widget_rebase.vue';
+import mountComponent from '../../helpers/vue_mount_component_helper';
+
+describe('Merge request widget rebase component', () => {
+  let Component;
+  let vm;
+  beforeEach(() => {
+    Component = Vue.extend(component);
+  });
+
+  afterEach(() => {
+    vm.$destroy();
+  });
+
+  describe('While rebasing', () => {
+    it('should show progress message', () => {
+      vm = mountComponent(Component, {
+        mr: { rebaseInProgress: true },
+        service: {},
+      });
+
+      expect(
+        vm.$el.querySelector('.rebase-state-find-class-convention span').textContent.trim(),
+      ).toContain('Rebase in progress');
+    });
+  });
+
+  describe('With permissions', () => {
+    beforeEach(() => {
+      vm = mountComponent(Component, {
+        mr: {
+          rebaseInProgress: false,
+          canPushToSourceBranch: true,
+        },
+        service: {},
+      });
+    });
+
+    it('it should render rebase button and warning message', () => {
+      const text = vm.$el.querySelector('.rebase-state-find-class-convention span').textContent.trim();
+      expect(text).toContain('Fast-forward merge is not possible.');
+      expect(text).toContain('Rebase the source branch onto the target branch or merge target');
+      expect(text).toContain('branch into source branch to allow this merge request to be merged.');
+    });
+
+    it('it should render error message when it fails', (done) => {
+      vm.rebasingError = 'Something went wrong!';
+
+      Vue.nextTick(() => {
+        expect(
+          vm.$el.querySelector('.rebase-state-find-class-convention span').textContent.trim(),
+        ).toContain('Something went wrong!');
+        done();
+      });
+    });
+  });
+
+  describe('Without permissions', () => {
+    it('should render a message explaining user does not have permissions', () => {
+      vm = mountComponent(Component, {
+        mr: {
+          rebaseInProgress: false,
+          canPushToSourceBranch: false,
+          targetBranch: 'foo',
+        },
+        service: {},
+      });
+
+      const text = vm.$el.querySelector('.rebase-state-find-class-convention span').textContent.trim();
+
+      expect(text).toContain('Fast-forward merge is not possible.');
+      expect(text).toContain('Rebase the source branch onto');
+      expect(text).toContain('foo');
+      expect(text).toContain('to allow this merge request to be merged.');
+    });
+  });
+});